A wide variety of products, from consumer electronics to battery-powered electric vehicles, utilize electrochemical energy sources. Batteries are devices which are capable of converting electrochemical energy into direct current and include a variety of electrochemical systems, such as AgO/Zn, Ag.sub.2 O/Zn, HgO/Zn, HgO/Cd, Ni/Zn, Ni/Cd, Ni/MH, and Zn/air.
Batteries are made up of one or more battery cells. In its most elementary form, a battery cell comprises a pair of electrodes, namely, an anode and a cathode, a battery separator, and an electrolyte. When a load is applied to the battery, electrons are generated through oxidation at the anode. The electrons thus generated pass through the load, then return to the battery cell at the cathode, where the cathode is reduced.
In such battery cells, the electrolytic solution, i.e., the solution containing the electrolyte, is the medium for mass transport between the electrodes. The primary functions of the battery separator are to prevent physical contact between the electrodes and to retain the electrolytic solution. In a starved-electrolyte battery cell, the separator completely occupies the space between the electrodes, and the electrolytic solution is completely contained within the battery separator. The battery separator thus functions as the reservoir for the electrolytic solution in such cells.
During the discharge and charge cycles of a battery cell, the physical dimensions of the electrodes can change, e.g., as a result of swelling. It is desirable that the separator, particularly in a starved-electrolyte battery cell, be resilient such that it can retain its capacity for electrolytic solution and maintain contact with the electrodes despite such dimensional changes. In addition, the battery separator should be spontaneously, uniformly, and permanently wettable in order to accommodate and fully retain the electrolytic solution, which is typically aqueous, e.g., 20-40 wt. % KOH or NaOH.
The present invention seeks to provide a battery separator which possesses these desirable characteristics. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.